Building a Simple Compost Heap That Works

Why a Compost Heap Is Worth the Small Effort

Few things in a British garden repay a modest amount of effort as generously as a compost heap. Give it a mix of grass clippings, prunings, vegetable peelings, torn-up cardboard and a few twiggy stems, and within a few months you will have a dark, crumbly, sweet-smelling material that works wonders dug into borders and vegetable beds. It improves soil structure, holds moisture through dry summers, feeds the worms and soil life beneath your feet, and saves you a small fortune in bagged compost. Best of all, a simple heap that actually works is not a technical exercise. It is really just a matter of layering the right materials in roughly the right proportions and letting nature do the rest.

Pick a Spot That Suits You and the Heap

Compost heaps are not fussy, but a little thought at the start saves bother later. Aim for a level, well-drained patch that gets some sun but is not baking all day — part shade is ideal, as it keeps the heap from drying out in July. You want it within easy reach of the kitchen door, because a heap you have to trudge to across a wet lawn in February is a heap that quietly stops being fed.

You do not need an expensive bin. A simple square enclosure made from four pallets wired together at the corners, or a ring of stakes wrapped with wire mesh, works beautifully and allows plenty of air in. If you garden on a small plot or a balcony, a lidded plastic bin or even a sturdy bag will do. A heap roughly one cubic metre in size — about a metre in each direction — heats up best, so build towards that if you can, and plan for two bays if space allows: one filling, one maturing.

The Golden Rule: Greens and Browns

Every successful heap rests on one simple idea. You are balancing two kinds of material, usually called greens and browns. Greens are soft, moist and nitrogen-rich. Browns are dry, tough and carbon-rich. Too many greens and the heap turns into a slimy, smelly mess. Too many browns and it sits there for years, barely breaking down. Get the mix roughly right — think of it as about two or three parts browns to one part greens by volume — and the whole thing takes care of itself.

Layer them as you go rather than tipping everything in loose. A good practical routine is a hand's depth of green material, then a couple of hand's depths of brown, then a scattering of something twiggy, and repeat. Twigs and small prunings are the secret weapon here: they create tiny air pockets throughout the heap, and without air the composting process stalls and turns sour.

What to include:

• Greens: grass clippings (spread thinly, never in thick mats), vegetable and fruit peelings, tea leaves and coffee grounds, spent annuals, soft hedge clippings, comfrey leaves and nettles.
• Browns: torn-up cardboard (remove tape and staples), scrunched newspaper, egg boxes, toilet roll tubes, dry autumn leaves, straw, wood shavings, and dead, woody stems.
• Extras that help: a thin sprinkle of soil or old compost every few layers, and a handful of lime on very acidic heaps.

Leave out cooked food if you are using an open heap, as it invites rats. Also avoid perennial weed roots such as bindweed and ground elder, diseased plant material, glossy printed magazines, and anything treated with weedkiller — these either survive the process or cause problems later.

Size Matters: Chop It Small

The single biggest improvement most gardeners can make is to cut things up. A whole cabbage stalk or a fistful of long twiggy prunings will sit in the heap for a year. Run a spade through tough stems, snap twigs into short lengths, tear cardboard into palm-sized pieces, and shred any branches thicker than a pencil. Smaller pieces give the bacteria far more surface area to work on, and your heap will heat up and finish in half the time. Keep a pair of old secateurs or a sharp spade by the bin and give things a quick chop as you add them.

Turning, Watering and Knowing When It Is Done

A well-built heap will heat up within a few days, and you may see steam rising on a cold morning. That warmth is a sign the microbes are working hard. To keep it going, turn the heap with a fork every three or four weeks, bringing the outside material into the middle and the middle out to the edges. Turning is not compulsory, but it speeds things along and lets you check the moisture.

Wring out a handful of the contents. It should feel like a damp sponge — moist but not dripping. If it is dry, water it as you turn. If it is sodden and smelly, fork in more cardboard and twigs and turn it again. Covering the heap with a piece of old carpet or a tarpaulin keeps rain out and warmth in, though you may want to leave it open during very wet spells.

Depending on the season, a heap turned regularly can be ready in two to three months in summer; a slower, unturned heap may take six to twelve months. It is ready when it looks like dark, crumbly soil, smells earthy rather than sour, and you can no longer recognise what went in. Sieve out any stubborn lumps and throw them back into the next heap. Then dig that black gold into your borders, spread it as a mulch around hungry plants like roses and beans, and start again — your soil, your plants and the worms beneath them will thank you for years to come.